1. Field of the Invention
The present invention relates to an electro-acoustic transducer such as a speaker, and more particularly to a speaker apparatus for bass reproduction.
2. Description of the Related Art
An electrodynamic speaker, half of which is shown in partial cross-sectional view in FIG. 1, is known as an electro-acoustic transducer. In this electrodynamic speaker, a pole yoke 1 projects from a center of a back plate, and a magnet 2 is provided around the pole yoke 1. A top plate 3 is located on the magnet 2 such that the top plate and pole yoke 1 in combination create a magnetic gap therebetween thereby forming a magnetic circuit. The top plate 3 is secured on a diaphragm 8 and a magnetic circuit frame 5. A voice coil bobbin 4 having a voice coil 4a wound thereon is oscillatably located in the magnetic gap, and is supported by a damper 7. A center portion of a cone-shaped diaphragm 8 is connected to the voice coil bobbin 4, and a center cap 6 is placed over a truncated portion of the cone-shaped diaphragm. A periphery of an opening of the diaphragm 8 is supported by the frame 5 via an edge 9. A lead of the voice coil 4a is connected to a terminal provided on the frame 5 by means of a colored cable.
As described above, in the electrodynamic speaker unit having a typical conventional drive, the voice coil is located in the magnetic circuit and an audio signal is input to the voice coil such that an electromagnetic force generated according to Fleming's left hand rule is used to drive the voice coil and in turn the diaphragm connected to the voice coil, thereby causing the air to oscillate.